A requirement exists in the fuel dispensing industry for a positive shut-off (zero leakage), fail-shut valve providing infinitely regulated fluid control in proportion to the amplitude or magnitude of an electrical input signal. Basically, such valves are required for controlling the flow of fluid fuels between 0 and 30 gallons per minute with a maximum working pressure of 150 p.s.i. Also, it is further required that the maximum pressure drop for such a desired valve be no more than one-half the working pressure when the valve is fully opened.
Known proportional flow control valves of the prior art do not meet the previously described requirement. Such known valves generally require much higher operating pressures, have excessive pressure drops, and do not provide positive shut-off, causing such valves to fail in an open condition.
There are many examples of efforts in the prior art to provide improved electrically-operated valves. In Neff U.S. Pat. No. 3,424,426, a solenoid 40, 50 is energized for lifting a needle 36 away from a metering orifice 25, permitting fluid under pressure in chamber 28 to escape from that chamber via the metering orifice 25. This in turn causes the pressure above the diaphragm 22 to decrease relative to the fluid pressure from the other side of the diaphragm from fluid in inlet 12, thereby causing diaphragm 22 to lift up, in turn permitting fluid from inlet 12 to flow into and be discharged from the outlet 13. When the solenoid 40, 50 is operated for permitting the needle 36 to again seat in the metering orifice 25, fluid entering the upper chamber 28 via a bleed orifice 26 creates a differential pressure imbalance, forcing the diaphragm 30 to seal about the sealing surface 15, closing the valve, thereby preventing fluid from inlet 12 to flow into outlet 13. A similar type valving mechanism using a flexible diaphragm is taught in Rattan, et al U.S. Pat. No. 3,655,163. Another similarly operating diaphragm valve is disclosed in Kozell, et al U.S. Pat. No. 3,872,878, and includes the addition of a spring biased plunger 27 for providing fail-shut operation of the valve.
Stampli U.S. Pat. No. 4,351,509 also teaches the use of a spring biased solenoid plunger with a diaphragm type valve for providing fail-shut operation (also see Zukausky U.S. Pat. No. 4,500,067). Note also that this patent teaches the use of a pilot valve seat 36 for positively sealing off the pilot flow passage 34 for closed valve conditions and for causing more rapid closure of the valve from an open valve condition.
Champeon U.S. Pat. No. 3,797,526 discloses a solenoid operated cage-type valve including a pilot controlled seal. Also shown is an "O"-ring seal 25 for a piston at the valve outlet, and another "O"-ring seal 26 between the side walls of the piston and the inside walls of the piston chamber.
Catania U.S. Pat. No. 3,633,868 discloses another form of piston valve including a solenoid operated pilot valve section for controlling the movement of a main piston in opening and closing the valve. Hertfelder, et al U.S. Pat. No. No. 4,270,726 teaches a solenoid operated pilot valve for a valve arrangement that includes a piston-like valve member coupled to a diaphragm above which is located a solenoid operated pilot valve plunger.
Solenoid operated proportional valves are also known in the prior art. For example, Arnold U.S. Pat. No. 3,926,405 teaches use of a solenoid operated armature for controlling the size of the valve opening by balancing the degree of energization of the solenoid against a countering spring force of a spring having a varying spring constant, thereby producing a valve opening proportional to a variable magnetic field produced by the solenoid. In Nishimiya, et al U.S. Pat. No. 4,314,585, another electromagnetically operated proportional type valve is disclosed, which incorporates a first spring tending to bias a valve open, a second spring tending to bias the valve closed, and an electromagnetically operated solenoid energizable for opening the valve, whereby the resultant effect of the closure and opening forces of the two springs causes valve operation to be porportional to the input current to the solenoid. Lastly, Odogaki, et al U.S. Pat. No. 4,428,558 discloses a proportionally operated rotary valve including a proportional solenoid having a rotary magnet for opening and closing a rotary valve in a proportional manner.